Optimization of Pore Structure of Cathodic Carbon Supports for Solvate Ionic Liquid Electrolytes Based Lithium–Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries are a promising energy-storage technology owing to their high theoretical capacity and energy density. However, their practical application remains a challenge because of the serve shuttle effect caused by the dissolution of polysulfides in common organic electrolytes. Polysulfide-insoluble electrolytes, such as solvate ionic liquids (ILs), have recently emerged as alternative candidates and shown great potential in suppressing the shuttle effect and improving the cycle stability of Li-S batteries. Redox electrochemical reactions in polysulfide-insoluble electrolytes occur via a solid-state process at the interphase between the electrolyte and the composite cathode; therefore, creating an appropriate interface between sulfur and a carbon support is of great importance. Nevertheless, the porous carbon supports established for conventional organic electrolytes may not be suitable for polysulfide-insoluble electrolytes. In this work, we investigated the effect of the porous structure of carbon materials on the Li-S battery performance in polysulfide-insoluble electrolytes using solvate ILs as a model electrolyte. We determined that the pore volume (rather than the surface area) exerts a major influence on the discharge capacity of S composite cathodes. In particular, inverse opal carbons with three-dimensionally ordered interconnected macropores and a large pore volume deliver the highest discharge capacity. The battery performance in both polysulfide-soluble electrolytes and solvate ILs was used to study the effect of electrolytes. We propose a plausible mechanism to explain the different porous structure requirements in polysulfide-soluble and polysulfide-insoluble electrolytes.

Three-dimensional ordered porous electrode materials for electrochemical energy storage

“…3DOP carbon as a substrate for sulfur cathodes is then utilized to couple with room-temperature IL electrolytes to further improve the immobilization of lithium polysulfides 129,130 . The dissolution of Li 2 S x was efficiently suppressed in the electrolyte comprising Nbutyl-N-methyl-piperidinium bis(trifluoromethanesulfonyl) amide 129 .…”

“…In terms of some solvate ILs, polysulfides are insoluble and tend to form an inhomogeneous layer that covers the 3DOP carbon surface. In this case, the more suitable structure should be the 3DOP carbon with both large macropores and a large volume instead of the widely accepted mesopores and/or micropores that work well for conventional polysulfide-soluble electrolytes 130 . Unfortunately, the cost of the IL electrolyte may render them impractical and uneconomical for applications.…”

A Micelle Electrolyte Enabled by Fluorinated Ether Additives for Polysulfide Suppression and Li Metal Stabilization in Li-S Battery

“…Also, polysulfide solubility may be reduced with an increase in lithium salt concentration as per the socalled common ion effect; (Vijayakumar et al, 2014) intuitively, one might imagine that pre-existing solvated Li + ions "use up" available coordination sites, leaving fewer remaining to interact with lithium polysulfides. As a result, high-concentration electrolytes i.e., room-temperature ionic liquids, (Park et al, 2013a,b;Song et al, 2013b) solvent-in-salt, (Suo et al, 2013), and solvate ionic liquids (Dokko et al, 2013;Ueno et al, 2013;Zhang et al, 2016) have all proven quite effective at discouraging polysulfide dissolution, despite their high viscosity and subsequent poor lithium transport properties. More recently, several researchers have addressed this problem through dilution of concentrated electrolytes with poorly-coordinating solvents; work reported by Weller et al demonstrated a low-density electrolyte with high lithium salt concentration to suppress polysulfide dissolution using hexyl methyl ether in combination with DOL (Weller et al, 2019).…”

Review of Carbon Materials for Lithium‐Sulfur Batteries

“…Since CMK‐3/sulfur composite cathode with improved cycling performance was synthesized successfully by Nazar and co‐workers in 2009, LSBs have possessed much significant breakthroughs. These enhanced works include some main aspects as follows: (i) novel batteries materials and structures such as composite cathode, functional binders, surface‐coated separators, and modified electrolytes; (ii) profound studies on the mechanism of redox reaction in LSBs during charge and discharge process; and (iii) new design approach in cell configuration …”